Downhole tools can be conveyed in multiple ways as they are lowered into the borehole or while drilling the borehole. Traditional approaches are the conveyance of the tool on wireline by lowering the tool on a cable that also provides power to the tool and communication between the tool and the surface. Alternatively, the tool can be conveyed by slickline. In this case, the tool is lowered on a cable that is used solely to convey the tool but does not provide power or communication. The tool functions in an autonomous way and has its own downhole power (typically batteries). Limited down communication can be achieved by accelerating the cable in a certain pattern. Tools can also be conveyed at the bottom of drill pipe (e.g., Tough Logging Conditions or “TLC”) if borehole conditions do not allow the tool to reach the bottom of the hole. This may be of particular interest in highly deviated or horizontal wells, where gravity will not allow the tool to reach the bottom of the well. In this kind of logging the wireline is inside the drill pipe and the logging therefore is very similar to traditional wireline logging.
Pushing tools down on a drill string may result in damage to the tools as they are used to push past obstacles in the wellbore. The operation of TLC is expensive and often requires logging cable and a logging truck. An alternative method is to deploy the tool through drill pipe, letting it exit the drill pipe and latch it to the bottom of the drill pipe. Once this is done, the drill pipe is pulled out of the hole while the tool is logging and recording the data in its internal memory.
In drill pipe conveyed logging, there may be little or no communication between the downhole tool and the surface. This poses several problems, many of which are due to the fact that the exact time at which the logging tool is latched to the bottom of the drill pipe is not known. In order not to exhaust the battery too early, the power to the tool should only be enabled once the tool is ready to log up.
Additional problems exist for pad density tools equipped with a caliper arm to eccentralize the pad and to measure the hole diameter or any similarly-equipped device with a caliper arm. These arms generally do not allow a tool to move down when they are open. If a tool is being pushed down with the caliper arm open, it may get stuck and with enough applied force the arm will bend or break.
It may be desirable, therefore, for the caliper arm to be opened only when the tool is ready to move up, which, in most cases, is a few minutes after it has been deployed. In the absence of any communication from the surface, it is not possible for the tool to detect whether deployment has been successful. According to conventional methods, the enabling of the tool power and opening of a caliper is generally based on a timer. This timer is set just before the tool is lowered into the drill pipe to be pumped down. The setting generally has to leave enough time to allow for the tool to be pumped down and deployed. As there can be multiple delays in the deployment this time has to be set very long (i.e., building in excess time). If the deployment is quick then there is a long wait after the deployment before the tool can start moving up.
Thus, needs in the art exist for systems and methods that address some of the deficiencies in conventional tools, such as some of the deficiencies described above.